Artificial leg

ABSTRACT

The artificial leg diclosed herein is adapted to be used in cases wherein the natural lower leg has been amputated in the knee joint. The stump formed by the natural upper leg is received in a socket member provided with a spherical outer surface at its lower end. A crescent-shaped carrier element, directly attached to the lower end of the socket member, is provided with a cylindrical top surface with a radius adapted to the radius of the spherical outer surface at the lower end of the socket member and with a cylindrical bottom surface having a smaller radius than the top surface. The bottom surface of the carrier element carries a cylindrical, backwardly sloping guide means. A sliding block is movable along said guide means and forms, together with the same, an artificial knee joint. An artificial lower leg is connected with, and exclusively supported by the sliding block. The carrier segment is dimensioned in such manner that the axis of the guide means is contained within the stump and lies below and behind the center point of the spherical outer surface of the lower end of the socket member.

Zevering Dec. 30, 1975 [54] ARTIFICIAL LEG [75] Inventor: Willem Zevering,'Weesp,

Netherlands [73] Assignee: Stichting Revalidatie Instituut Muiderpoort, Amsterdam, Netherlands 22 Filed: Feb. 14,1975

21 Appl. No.: 550,132

[30] Foreign Application Priority Data Primary ExaminerRonald L. Frinks Attorney, Agent, or Firm-Haseltine, Lake & Waters [5 7] ABSTRACT The artificial leg diclosed herein is adapted to be used in cases wherein the natural lower leg has been amputated in the knee joint. The stump formed by the natural upper leg is received in a socket member provided with a spherical outer surface at its lower end. A crescent-shaped carrier element, directly attached to the lower end of the socket member, is provided with a cylindrical top surface with a radius adapted to the radius of the spherical outer surface at the lower end of the socket member and with a cylindrical bottom surface having a smaller radius than the top surface. The bottom surface of the carrier element carries a cylindrical, backwardly sloping guide means. A sliding block is movable along said guide means and forms, together with the same, an artificial knee joint. An artificial lower leg is connected with, and exclusively supported by the sliding block.'The carrier segment is dimensioned in such manner that the axis of the guide means is contained within the stump and lies below and behind the center point of the spherical outer surface of the lower end of the socket member.

4 Claims, 2 Drawing Figures US. Patent Dec. 30, 1975 1 ARTIFICIAL LEG BACKGROUND OF THE INVENTION The invention relates to an artificial leg which is adapted to be used in cases wherein the natural lower leg has been amputated in the knee joint.

German Pat. No. 350,688 discloses an artificial leg, comprising a socket member for receiving the stump formed by the natural upper leg, the lower end of said socket member being connected to a curved, backwardly sloping guide means, on which a curved sliding block is movably mounted, which sliding block is connected with an artificial lower leg carrying a foot, said sliding block together with said guide means forming an artificial knee joint.

The known artificial leg has the disadvantage that it can only be used in those cases wherein the patients leg has been amputated in the upper part of the leg, well over the knee.

As compared to an amputation above the knee an amputation of the lower leg in the knee joint has, in regard to an artificial leg, the advantage of a longer stump, which enables a very stable connection between the stump and the socket member of the artificial leg, whereas the muscles of the upper leg remain totally intact so that they may maintain the normal functions. Apart from that the natural lower end of the thigh-bone may be, unlike the sharp end of the severed thigh-bone, vertically placed under load, and it also forms a larger and stronger load bearing surface.

However, the amputation of the lower end at the knee joint has the disadvantage that it is extremely difficult to furnish the artificial leg with a knee joint, of which the center of rotation lies at the desired level, namely at the same level as the center of rotation of the original natural knee joint. Because the artificial knee joint has to be placed underneath the lower end of the socket member, the center of rotation of this joint will lie at a relatively large distance below the lower end of the thigh-bone, whereas the natural center of rotation lies immediately over the lower end of the thigh-bone. This distance is, apart from the thickness of the wall of the socket member, determined by the size of the artificial knee joint. In case of an amputation above the knee the thigh-bone is usually severed at about 12 cm above the knee, in order to be able to bring the center of rotation of the artificial knee joint at the natural level.

If the center of rotation of an artificial knee joint does not coincide with the natural center of rotation, walking is made more difficult by the unnatural swinging movement of the artificial lower leg and the artificial leg will, especially when the patient is in a sitting position, assume a very conspicuous unaesthetic ap pearance, which is cosmeticably unacceptable and extremely unpleasant for the patient.

For these reasons amputations of the lower leg at the knee joint are, in spite of the described advantages and of a very simple mode of operation, never or at least hardly ever performed.

BRIEF SUMMARY OF THE INVENTION The invention has as its object to supply an artificial leg adapted to be used in cases wherein the natural lower leg has been amputated in the knee joint and provided with an artificial knee joint having a center of rotation that coincides substantially with the center of rotation of the natural knee joint and closely simulating 2 the physiological movements of the natural knee, said artificial leg also being very strong and of simple construction.

According to the invention this object is realized with an artificial leg of the kind described, by providing a spherical lower end of the socket member with a radius larger than the radius of the cylindrical guide means, said guide means being provided on the outer surface of a crescent-shaped carrier segment, of which the inner surface has a radiusadapted to the lower end of the socket member, said carrier segment being directly fastened to the lower end of the socket member and dimensioned in such manner that the axis of the guide means is contained within the stump and lies under and behind the center point of the lower end of the socket member, and said lower leg being exclusively supported by the sliding block, all this in such manner, that the artificial leg may be used in case the natural lower leg is amputated in the knee joint.

Thus, it is assured that the center of rotation of the artificial knee joint exactly coincides with the center of rotation of the natural knee and also that, when the leg is stretched, the axis of the lower leg does not pass through the center point of the lower end of the socket member. The latter is very important. If namely, when the leg is stretched, the workline of the force with which the loaded lower leg bears on the lower end of the socket member, passes through the center point of the lower end of the socket member, which would be inevitable if the guide means is concentric with the lower end of the socket member, the sliding block is placed in a labile position, in which the tendency of the sliding block to move along the guide means is equally large in both directions, so that there is a substantial danger that the knee joint will be bent in the wrong direction. With the artificial leg according to the invention the tendency of the sliding block to move in the direction commensurate with the natural bending of the knee is much greater, thanks to the described eccentricity. Besides, with the artificial leg according to the invention, when it is bent, a relative shortening of the leg is obtained, which is also the case with the natural knee joint and prevents the foot from touching the ground, when the lower leg swings forwards.

The use of a crescent-shaped carrier segment has the important advantage that regardless of the age and the size of the patient, the size, the shape and the radius of curvature of the guide means, and therefore also those of the sliding block, are always the same, so that only the inner surface of the carrier segment has to be adapted to the shape and the size of the socket member. This means of course a substantial simplification of the fabrication of the artificial leg, which also leads to a substantial decrease of the fabrication costs.

In case the artificial leg is provided with a brake lining, which immobilizes the artificial knee joint when a load bears on the lower leg, it is of advantage to shape the guide means as a guiding rail with a T-shaped cross section and to provide the sliding block with a corresponding channel, in which the guiding rail is received with such play, that the sliding block, when the lower leg is not loaded, is movably supported by the flanges of the guiding rail, whereas the guiding rail, when the lower leg is loaded, is pressed on a brake lining provided on the bottom of the channel. Preferably the lower surface of the guiding rail is provided with a guiding groove, in which a cam, provided on the bottom of the channel, is received, in order to resist trans- 3 ,versely directed forces and to prevent axial rotation of the lower leg.

Finally it is advantageous to provide the lower surface of the guiding rail with a layer of wear-resistant material.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a side view of an artificial leg according to the invention.

FIG. 2 shows a sectional view of the artificial leg taken along the line II-II in FIG. 1.

DETAILED DESCRIPTION The artificial leg shown in the drawings comprises a socket member 1 for receiving a stump 2 formed by the upper leg after amputation of the lower leg in the knee joint. The socket member is pivotably connected with an artificial lower leg 4 carrying a foot 3, by means of an artificial knee joint, which will be described in detail herein below.

The center point 5 of the spherical lower end of the socket member 1 lies above the lower end of the thighbone 6. The socket member 1 is adapted to the shape of the stump 2 and provided with a soft lining material 7, so that the lower end of the stump, formed by skin flaps folded over the end of the thigh-bone, is supported on all sides.

The knee joint of the artificial leg consists of a curved guiding rail 8 with a T-shaped cross section, which forms the outer surface of a crescent-shaped carrier segment 9, which is attached to the lower end of the socket member 1 and of a sliding block 10 movably mounted on the rail 8 and carrying the lower leg 4. In order to attain a strong connection between the carrier segment and the socket member 1 a supporting plate 1 1 is provided within the lower end of the socket member l.

The guiding rail 8 has a constant curvature and the center 12 of curvature of the guiding rail does not coincide with the center point 5 of the lower end of the socket member 1, but lies at a distance below and behind this center point 5. The radius of curvature of the inner surface of the carrier segment 9 is adapted to the curvature of the socket member 1 and the remaining space between the segment 9 and the lower end of the socket member is filled with a filling material 13.

Because of the eccentricity of the carrier segment it is assured on the one hand that the sliding block 10, when the artificial leg is loaded, preferably moves in the direction corresponding with the natural bending of the knee, namely backwards along the guiding rail 8, and on the other hand that the center of rotation of the artificial knee joint, which coincides with the center of curvature lies close to the lower end of the thigh-bone 6, as is the case with the center of rotation of the natural knee joint.

The sliding block 10 is provided with a T-shaped channel in which the guiding rail 8 is received with some play, so that when the leg is not loaded the sliding block 10 is supported by the flanges of the guiding rail 8 and can freely move along the guiding rail when the leg is swung forward. On the bottom of the channel of the sliding block 10 brake linings 14 are provided, so that the lower surface of the guiding rail 8, which may be covered with a wear-resistant material 15, is pressed on the brake linings 14 when the leg is loaded, thereby 4 preventing the sliding block 10 from moving along the guiding rail 8.

On the bottom of the channel of the sliding block 10 an upwardly extending cam 16 is provided, which is movably received within a groove 17 in the lower surface of the guiding rail 8 in order to resist laterally directed forces bearing on the kneejoint and to prevent axial rotation of the lower leg 4. The guiding rail 8 is further provided with a stop 18 for the sliding block 10 at the forward edge, preventing overstretching of the leg, when it is swung up. I

The lower leg 4 is provided with a mounting plate 19 attached to the sliding block 10 by means of screws 10a. The socket member 1 also is attached to the carrier segment 9 by means of screws 9a. Because the inner surface of the carrier segment is adapted to the shape of the spherical lower end of the socket member, the segment may exactly be brought into the desired position relative to the socket member.

The carrier segment is preferably made out of a plastic material, so that the artificial leg has the advantage of a relatively low weight.

I claim:

1. An artificial leg adapted to be used in cases wherein the natural lower leg has been amputated in the knee joint, comprising a socket member adapted to receive the stump formed by the natural upper leg and provided with a spherical outer surface at its lower end, a crescent-shaped carrier segment directly attached to the lower end of said socket member, having a substantially cylindrical top surface with a radius adapted to the radius of said spherical outer surface and a substantially cylindrical bottom surface having a smaller radius than said top surface, a cylindrical, backwardly sloping guide means provided on said bottom surface and having a radius smaller than the radius of said spherical outer surface, a sliding block slidably mounted on said guide means and forming, together with the same, an artificial knee joint, and an artificial lower leg, connected to and exclusively supported by said sliding block, said carrier segment being dimensioned in such manner that the axis of said guide means is contained within the stump and lies below and behind the center point of said spherical outer surface.

2. An artificial leg as claimed in claim 1, further comprising a brake lining for immobilizing said artificial knee joint when the artificial lower leg is loaded, wherein said guide means is formed as a guiding rail having a T-shaped cross section, said sliding block has a correspondingly shaped guiding channel, and said brake lining is attached to the bottom of said guiding channel, said guiding rail being received in said guiding channel with such play that said sliding block is freely movable along the flanges of said guiding rail when the lower leg is not loaded, whereas the guiding rail is pressed on the brake lining when the lower leg is loaded.

3. An artificial leg as claimed in claim 2, wherein a groove is provided in the lower surface of said guiding rail, and a cam is provided on the bottom of said guiding channel, said cam being received in said groove.

4. An artificial leg as claimed in claim 2, wherein the lower surface of said guiding rail is provided with a layer of a wear-resistant material. 

1. An artificial leg adapted to be used in cases wherein the natural lower leg has been amputated in the knee joint, comprising a socket member adapted to receive the stump formed by the natural upper leg and provided with a spherical outer surface at its lower end, a crescent-shaped carrier segment directly attached to the lower end of said socket member, having a substantially cylindrical top surface with a radius adapted to the radius of said spherical outer surface and a substantially cylindrical bottom surface having a smaller radius than said top surface, a cylindrical, backwardly sloping guide means provided on said bottom surface and having a radius smaller than the radius of said spherical outer surface, a sliding block slidably mounted on said guide means and forming, together with the same, an artificial knee joint, and an artificial lower leg, connected to and exclusively supported by said sliding block, said carrier segment being dimensioned in such manner that the axis of said guide means is contained within the stump and lies below and behind the center point of said spherical outer surface.
 2. An artificial leg as claimed in claim 1, further comprising a brake lining for immobilizing said artificial knee joint when the artificial lower leg is loaded, wherein said guide means is formed as a guiding rail having a T-shaped cross section, said sliding block has a correspondingly shaped guiding channel, and said brake lining is attached to the bottom of said guiding channel, said guiding rail being received in said guiding channel with such play that said sliding block is freely movable along the flanges of said guiding rail when the lower leg is not loaded, whereas the guiding rail is pressed on the brake lining when the lower leg is loaded.
 3. An artificial leg as claimed in claim 2, wherein a groove is provided in the lower surface of said guiding rail, and a cam is provided on the bottom of said guiding channel, said cam being received in said groove.
 4. An artificial leg as claimed in claim 2, wherein the lower surface of said guiding rail is provided with a layer of a wear-resistant material. 